Robot balances on a ball

07 June, 2012

A team of Swiss students has developed a robot which balances on a sphere and can accelerate instantly in any direction. The Rezero “ballbot” can respond within thousandths of a second, accelerate at 3m/s², hit a top speed of 3.6m/s, and lean at angles of up to 20 degrees without toppling over.

The robot (shown above, with and without its covering) makes constant minute adjustments to keep its centre of gravity perfectly positioned. To move, it performs a “controlled fall” in the desired direction of travel, and applies the exact amount of drive to the ball to hold it at a constant angle. It stops by outrunning itself, counteracting the forward momentum and bringing its body upright. The robot is so responsive that its creators have incorporated a game mode in which bystanders can push it around.

Drive to the ball is delivered via three specially-developed “omniwheel” assemblies that allow a complete range of axial and radial rotation. To help specify a drive that would deliver the speed, torque and rapid responses needed to maintain balance, within the limited space of the omniwheel housing, the developers called in engineers from maxon motor.

Together, the teams devised a combination of a four-pole DC brushless motor with a 42mm planetary gearhead and encoder that offered the required torque and responsiveness. Positioning control is provided by maxon’s Epos 70/10 modules.

“The potential for such a device is huge,” says maxon motor senior sales engineer, Ian Bell. “The developers have proposed it could be used as medical transportation, an automated photographer, a tour guide, or even a toy. One thing is clear – while Rezero is truly one of a kind, it is likely the first of many.”